Basically, roof windows may be provided in a number of varieties and include more or less complicated structures in order to allow opening of the sash and to fulfil other functions, such as ventilation, while permitting cleaning of the outside of the pane from inside the building. The varieties include roof windows of the pivoting type, the hinge axis being either located at the centre or displaced from the centre of the window, and top-hung roof windows that pivot for cleaning by means of an intermediate frame.
These requirements are made possible by the provision of a hinge with a particular pattern of movements, which in turn makes it possible to establish an overlap between the cover members fastened to the frame and the counterpart cover members fastened to the sash in the closed position of the roof window.
One very well-proven type of hinge is the pivot hinge including a guidance on the frame hinge part cooperating with a slide rail on the sash hinge part. Such pivot hinges are for instance disclosed in Applicant's EP 1 038 083 B1 and EP 1 781 883 B1, and are very versatile as regards operational areas and adaptation of components. Examples of roof windows incorporating such adapted hinges are shown in Applicant's published European patent applications EP 2 770 146 A1 and EP 2 770 149 A1.
However, as the traditional pivot hinges to some extent rely on frictional forces to operate correctly, it is desirable to utilize an alternative configuration of the hinge in certain fields of application, in which the desired pattern of movements is provided by a linkage mechanism. The use of hinges including linkage mechanisms is traditionally most often known from the furniture field, but such hinges are also well-known to use for roof windows. Prior art examples include Danish patent No. 114 321, U.S. Pat. No. 4,446,597, and Applicant's European patents EP 22 657 B1 and EP 89 813 B1. The latter document discloses a hinge of the kind mentioned in the introduction.
Although the linkage mechanisms in the above examples are to some extent capable of providing the kinematic pattern and force transmission aimed at, there is still room for improvement.